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On Wed, 1 Jun 2016 18:05:17 +0000 (UTC), M0ELS wrote:
>Can some please shed some light as to why this is not working and how to solve
>it
REPLY:
It sounds like the output tank circuit is simply not resonant on 160
meters, or if it is resonant, the impedance matching ratio is way off.
I would suggest two things to do:
1. Download the GM3SEK impedance matching spreadsheet from:
http://www.ifwtech.co.uk/g3sek/ and spend some time figuring out what
the values for the pi network should be.
2. Once you have the correct values in place, use an SWR analyzer such
as an MFJ-259 series to resonate the pi network tank circuit. You do
this by removing all power from the amplifier and connecting the
analyzer to the output of the pi network. If there is a T/R relay,
close it or jumper around it. Connect a non-inductive resistor from
the anode of one of the tubes to ground, the value of which is equal
to the plate impedance of the tubes. With the analyzer set to 160
meters, you should be able to get a 1:1 SWR by adjusting the tune and
load controls. Assuming you have the correct value of resistor, that
will be the same setting when transmitting.
Don't forget to remove the resistor when done!!
That should be enough to solve the problem. Feel free to ask if you
have more questions.
73, Bill W6WRT
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